Elphinstone and Erskine: SP or CP?

There is an apparent slight lacuna in SP vols III and V, published in
1906 and 1908, which is avoided in CP volume V published in 1926. My
normal view, in default of anything else is to take the later research.
Anyhow here's the details:

In SP III, p. 532 in the Elphinstone article it states that Alexander,
2nd lord Elphinstone, d. 1547, m. Catherine Erskine dau. of John, 4th
lord Erskine and his wife Isabel, dau. of Sir George Campbell.

But in SP V, pp. 608-9 in the Erskine/Mar article it states that, the
4th lord Erskine, d. 1513 at Flodden, was _Robert_ and he did indeed
marry Isobel, daughter of Sir George Campbell of Loudon, but they did
not have a daughter Catherine.

Over the page in SP V, 609-612, John, 5th lord Erskine, d. aft 1555,
is said to have m. Margaret, eldest dau. of Archibald, 2nd earl of
Argyll and they did have a dau. Catherine who m. in Nov 1525
Alexander 2nd lord Elphinstone.

CP is at least consistent:

In CP V, p. 57, Alexander, 2nd lord Elphinstone, d. 1547 at Pinkie, m.
Katherine da. of Robert (Erskine) 4th lord Erskine and Isabel dau. of
Sir George Campbell.

In CP V, p. 105, Robert, 4th lord Erskine, d. 1513 at Flodden, m.
Isabel, 1st da. of Sir George Campbell of Loudon.

Anyone got any views on who might be right about the father-in-law of
Alexander, 2nd lord Elphinstone? There's no CP corrections on Chris
Phillips' site nor in CP XIV, nor can I find anything in the archives.